1. Field of the Invention
The present invention relates to a control device for a vibration type motor which is used as a driving source for a video camera or video camera lens, and relatively drives a vibration member and a contact member in contact with the vibration member using a travelling vibration wave generated on the surface of the vibration member by applying a periodic voltage to an electromechanical energy conversion element such as an electrostrictive element or piezoelectric element.
2. Related Background Art
A conventional control device for a vibration type motor is constituted as shown in FIG. 18. FIG. 18 shows the case in which the vibration type motor controls the lens position of a camera.
Referring to FIG. 18, a D/A convertor 203 converts a digital output signal from a microcomputer (CPU) 202 into a voltage output. A VCO 204 outputs a periodic voltage corresponding to the output voltage obtained by the D/A convertor 203.
A frequency divider and phase shifter 205 divides the frequency of the periodic voltage output from the VCO 204 to output rectangular waves A and B having a phase difference of xcfx80/2 between them. An input power amplifier 206 amplifies the periodic voltage from the frequency divider and phase shifter 205 to a voltage and current capable of driving a vibration type motor 207. The vibration type motor 207 generates a travelling vibration wave on the surface of a vibration member by the periodic voltages A and B applied from the input power amplifier 206, thereby rotating a moving member (contact member) in contact with the vibration member.
An encoder 209 is mechanically connected to a lens 208 together with a counter 210 to detect the moving amount of the lens 208. A comparator 211 detects the phase difference between a sensor electrode S incorporated in the vibration type motor 207 and the applied periodic voltage A to inform the CPU 202 of a resonance state of the vibration type motor.
The CPU 202 calculates the difference between target position information indicated by a command signal generator 201 and position information of the lens 208 obtained by the counter 210, and outputs a digital signal to the D/A convertor 203 so as to make the lens position coincide with the target position.
FIG. 15 shows the relationship between the lens moving speed and the lens position. The lens moving speed changes in a trapezoidal shape using the maximum speed as an upper side with respect to target position information from the command signal generator 201. Referring to FIG. 18, the CPU 202 calculates the difference between target position information indicated by the command signal generator 201 and position information of the lens 208 obtained by the counter 210, and gradually increases the moving speed to keep the maximum speed for a given period. As the lens position comes near the target position, the CPU 202 outputs a digital signal to the D/A convertor 203 so as to decrease the moving speed to make the lens position coincide with the target position.
FIG. 15 shows the case wherein the start position is sufficiently distant from the target position. For a short distance, the moving speed does not reach a set maximum speed.
However, conventional control may fail due to changes in resonance characteristics of the vibration type motor.
FIG. 19 shows conventional control together with the characteristic of the vibration type motor. In FIG. 19, the motor rotational speed characteristic is hilly with respect to the frequency along the abscissa. At position ∘ on this hilly characteristic, a stable maximum speed is attained. The left driving frequency range from the peak of the hilly characteristic is not suitable for control because the motor speed abruptly decreases.
To actuate the vibration type motor, the frequency is gradually decreased from a start-up frequency fo to increase the speed. Since control becomes difficult for the speed at position ∘ or higher, the speed has conventionally been limited not to lower a frequency fh (at position ∘) for obtaining a maximum speed Vmax by storing the frequency fh in the memory of the control device.
In this way, the speed limit frequency must be conventionally used to obtain the maximum driving speed under stable control, which complicates the control. In addition, the vibration type motor actually starts rotating at different start-up frequencies depending on the temperature. If the start-up frequency is set regardless of the temperature, the time to start activation becomes long.
When a plurality of vibration type motors are controlled at a common maximum speed, variations in maximum speeds of the motors may cause a failure at the same maximum speed.
One aspect of the application is to provide a control device for a vibration type motor which relatively drives a vibration member excited to vibrate by electromechanical energy conversion, and a contact member in contact with the vibration member, comprising temperature detecting means for detecting a temperature of the vibration type motor, and speed setting means for setting a maximum driving speed of the vibration type motor in accordance with the temperature detected by the temperature detecting means, wherein driving is controlled using the set speed as an upper limit.
One aspect of the application is to provide a driving device for a vibration type motor in which a periodic signal is applied to an electromechanical energy conversion element portion arranged on a vibration member to obtain a driving force, comprising temperature detecting means for measuring a temperature of or near the motor, frequency setting means for setting an initial frequency of the periodic signal upon actuating the motor to a frequency corresponding to the temperature detected by the temperature detecting means, and control means for shifting the frequency from the set frequency to a lower frequency to actuate the motor.
One aspect of the application is to provide a driving device for a plurality of vibration type motors in which periodic signals are applied to an electromechanical energy conversion element portion arranged on a vibration member of each motors to obtain a driving force, the driving device driving the motors at a common maximum speed, comprising speed information setting means for setting, as a maximum speed common to the motors, the lowest speed out of speeds of the motors when a frequency of the periodic signal for each motor becomes higher than a resonant frequency or a frequency near and higher than the resonant frequency, and control means for controlling the speed of each motor using the speed set by the setting means as a maximum speed.
The above and other objects of the present invention will be apparent from the following description in conjunction with the accompanying drawings.